Typically, the major components of a wind turbine, such as blade, nacelle, tower, or hub, are transported to the installation site to be installed there. The connecting portions of these components which allow interconnection are important for a secure connection with other components but usually sensitive to the outside environment, therefore these connecting portions are usually protected by various means in the factory such as oil, cover etc. and then exposed at site for installation.
However, when the components arrive at the site and then the current corrosion prevention structure of the connecting portion is removed, a small amount of corrosion may appear even just during the short time of installation. Given that wind turbines are designed for a 20-year or even longer life time, even a small amount of corrosion occurring during installation is undesirable, in particular for offshore projects where environment is particularly severe, issue of corrosion during installation are problematic.
As an example, blades are usually connected to the hub via inserts secured in the blade root section. Even if a small amount of corrosion exists in the inserts, when the blade is mounted on the bearing there is a risk that corrosion will grow into the endface of the insert and/or the bond line between the insert and the bearing surface. That will reduce the strength of the connection. It is possible to use stainless steel for the insert, but due to the large number of the inserts for large blade, the cost will significantly increase.